What is the ideal way to discover new drugs?

Introduction-what invertebrate are used as models.

Advantages for-what information has been gained from these models? Specific examples of diseases where advance have been made using these models.

Disadvantages-what information isn’t possible to gain from these models that would be relevant to human? Are there any example where mechanism discovered in these models are not the same when work has been done in animal studies or human.

Conclusion in your opinion how relevant are these invertebrates models? What other model systems are used to develop new drugs? What is the ideal way to discover new drugs?
The models would be:
1-C elegant
2-Drosophila
The example would be:
1-Cancer
2-Ageing
3-Diabetes , insulin metabolism
4-Wound healing

Be aware of two things:
1-Be specific not write in general, be convincing.
2-I need the structure very simple because Im not native speaker.